The present invention relates to a seat reclining mechanism. In our UK patents 1528357 and 1586869 we disclose a seat reclining mechanism which includes a cushion arm pivotally connected to a squab arm by a planetary gear arrangement. The planetary gear arrangement includes a pair of side by side ring gears, one being secured to the squab arm and the other being secured to the cushion arm. A sun gear is provided which is in driving connection with both ring gears via a plurality of planetary gears. The pitch of teeth in each of the ring gears is different so that rotation of the planetary gears causes relative rotation between the ring gears.
The planetary gears float and it is necessary for there to be an acceptable amount of tolerance between the gears in order to enable smooth operation. Unfortunately such tolerance also results in pivotal play between the squab and cushion arms.
According to the present invention there is provided a seat reclining mechanism including a cushion arm pivotally connected to a squab arm by a planetary gear arrangement, the planetary gear arrangement including a pair of side by side ring gears, one of the ring gears being secured to the squab arm and the other of the ring gears being secured to the cushion arm, a sun and planetary gear arrangement common to both ring gears, the sun and planetary gear arrangement including a plurality of radially movable planetary gears surrounding a sun gear assembly, the sun gear assembly including at least one axially movable frusto-conical sun gear in engagement with said planetary gears, the at least one frusto-conical sun gear being axially biased so as to bias sun gear member into full meshing contact with the planetary gears and thereby bias the planetary gears in a radially outwards direction to a radially outermost position whereat the planetary gears are in full meshing contact with said ring gears, the sun gear assembly including a stop sun gear axially juxtaposed to said frusto-conical sun gear, said stop sun gear being in partial meshing contact with said planetary gears when at their radially outermost position such that the planetary gears are able to move radially inwards against said bias to a radially innermost position defined by the stop sun gear whereat the planetary gears are in full meshing contact with said stop sun gear.
Accordingly when the sun gear assembly is static pivotal play between the squab arm and cushion arm is substantially reduced or eliminated by virtue of the planetary gears being radially biased outwardly into contact with the ring gears by the frusto-conical sun gear. In addition, when under radial loading, as for example when the sun gear assembly is driven, the planetary gears are able to move radially inwardly into full mesh with the stop sun gear. This provides a positive smooth drive from the sun gear assembly to the planetary gears.
Preferably a pair of frusto-conical sun gears are provided arranged with their smaller diameter axial ends facing one another and such that they are located on opposite axial sides of the planetary gears. The biasing means are arranged such as to urge the two frusto-conical sun gears axially toward one another. This may be achieved by having one frusto-conical sun gear axially fixed and the other axially movable or both frusto-conical sun gears may be axially movable.
Preferably three planetary gears are provided which are equally spaced about the internal circumference of the ring gears. Three planetary gears are preferred since such an arrangement ensures that each sun gear will apply an equal radial loading on each planetary gear. However it is to be appreciated that more than three planetary gears may be provided if necessary.
The mechanism may also include at least one support member for the planetary gears of the type disclosed in our UK patent 1586869. Thus the support member would include for each planetary gear a concave surface.
In the present invention, the support member serves primarily to maintain the circumferential spacing of the planetary gears whilst the planetary gears are located between their radially inner and outermost positions. Preferably the support member is arranged to supplement accommodation of radially inwardly directed loadings when the planetary gears are located at their radially innermost positions. Such an arrangement enables the mechanism to withstand excessive radially inwardly directed loadings as may for example arise during a vehicle crash.
Preferably the included angle between the inclined peripheral face of each frusto-conical sun gear and its axis is small, for example in the range 2xc2x0 to 15xc2x0.
Preferably the frusto-conical sun gear, stop sun gear and planetary gears have involute teeth. This facilitates smooth operation of the mechanism.
The frusto-conical sun gear and stop sun gear may be separate components located axially side by side, or alternatively the frusto-conical sun gear and stop sun gear may be integrally formed.